A I R 



A IR 



receiver ; the fyphon-gage y is mnde in the ufual manner ; 

 but the cillerns x, x, prevent the gages from being dirtied 

 by the oil, on the readinifTion of the air. The large barrel 

 C has a lolid plunger, worked by the rod R, which pafTes 

 through the collar of leathers u ; for the conilruftion of 

 which, as well as the internal llruiture of the barrel C, fee 



■fis- 47- . 



This is a vertical feflion of the barrel, &c. ; the top or 

 cup U fcrews on to the fcrevv it, and the cavity h is made 

 conical ; the holes e, e, are made jull large enough to let 

 the pifton rod pafs freely ; the cavity h is filled with circular 

 greafed leathers, through the center of which a hole is 

 made, that barely admits the pillon rod to pafs j thefe 

 leathers are croudcd into A, and three or four thiekuefles of 

 them are left above the furface, f; and confequently, when 

 the cup U is ierewcd down, ihcfe leathers are forced into 

 the fmaller part of the cor.ical hollow /i ; and therefore they 

 bind as much or as little as is requifite on the pillon rod. 

 The head a is fcrevvcd with eight fcrews on the upper 

 flaunch or pait of the barrel C ; the bottom B fcrews on 

 the lower flaunch or lower end of C ; the plug D is accu- 

 I rately ground into a conical hole in the bottom B and has 

 I the lever L Handing at right angles. As the whole nicety 

 [ of the cxhauftion of this air-pump depends upon this part, 

 it fhould be very particularly defcribed. The lever L is re- 

 prefented as (landing to the left hand ; and the hole z with 

 its valve l is feen in connettion with the pipe P, and confe- 

 quently with the receiver ; fee the horizontal ftdtion L D 

 P. But if the lever L is brought towards the word 

 " CLOSED," the hole 2 with its valve l has moved onwards 

 towards D ; no hole is oppoiite to the hole of P, and con- 

 fequently all communication between the receiver and the 

 inlide of the barrel C is cut off ; but upon moving the lever 

 L more towards the right hand, the hole 3 having " no 

 valve" will be in conneftion with P, anj confequently 

 there will be a direft or uninterrupted pafTage between the 

 receiver and the infide of the barrel C. Upon attentively 

 infpefting the fe&ion, it will be perceived by the direftions 

 in which the valves open and clofe, and the poiition of the 

 paffages which are drilled through the thicknefs of the 

 . barrel, that the afcent or defcent of the folid plunger N 

 equally exhaulls the pipe P, and confequently the receiver. 

 It muil be remarked, that the valves exhibited in the feAion 

 are drawn like lids of boxes, with joints for the purpofe of 

 fhcwing in what dircilion they open ; but in realitv the 

 valves are made of oiled filk ; and as on the nice conlhucl;ion 

 of thefe tiie good ailition of the pump much depends, the 

 bed mode of making them will be illuilratcd in the fcition, 

 fy. A A, which lliews the plug D, on which the valve is to 

 be fixed. In the iirft place, a groove muft be turned, of a 

 convenient fize, fo as to leave a cylindrical knob F, whofe di- 

 ameter may be four or five eighths, or more, of an inch ; the 

 hole which the oiled filk valve is intended to cover, is made 

 through the axis or center of this knob, as is (hewn by the 

 dotted lir.es H ; the ring G is to fit nicely into the groove, and 

 to be fluih with the general fnrface of the brafs ; the furface 

 of the knob V muil be turned away about double the 

 thicknefs of the oiled filk for the purpofe of preferving the 

 oiled filk from injury by the pifton's linking it ; a flip of 

 oiled filk about the width of four times the diameter of the 

 hole, which it is to cover, mull he laid over the hole in the 

 center of the knob F, and the ring G carefully put in its 

 place and there fixed by two or three fcrews. Fig. B B 

 fliews the conllrudlion of the refcnoir x x, (fig. 46,), for the 

 piirpofe of keeping the gages clean. The end of the gage 

 G, for inftance, paffes through the bottom of the refer\-oir 

 X, and reaches nearly to the top ; and a piece of metal, flat 

 Vol. I. 



or like an inverted tea-fauccr, is fixed to the top of ic, ^g. 

 B B. The oil which comes from the pump through m is 

 thrown on the back of the faucer, and running to its edges 

 drops into the bottom part of the rcfcrvoir, and thus prevent* 

 any filth from getting into the tube G, /i^. 46. 



Having defcribed the particular parts of this pump, we 

 fliall next explain the mode of working it, fo as to obtam the 

 great I'll degree of exhauHion. A receiver well ground and 

 made diy, w ith oil put upon its edge, is to be placed on the 

 pump plate T, (fig. 46.), over the aperture of the pipe P ; 

 and the lever L is to be moved fo as to Hand under the word 

 " valve." By working the pillon of the cylinder C up 

 and down, from the top to the bottom, the receiver becomes 

 partly exhaulled, and the mercury will rife from the cillem 

 M up into the tube of the barometer gage G ; the exhauilion 

 mull be continued till it will rife no higher ; and turning the 

 lever L under the word " closed," the pillon mull be 

 moved two or three times up and down ; let it then be left 

 at the bottom of the barrel C ; move the lever L under the 

 words " NO valve," and gently ra;fe the pillon to the top 

 of the baiTcl. As there is now a direft communication be- 

 tween the receiver and the barrel C, without the intervention 

 of a valve, the air will expand itlelf freely into the barrel, 

 and the mercury of the gage will rife ; keeping the pifton 

 at the top of the barrel, turn the lever again under the word 

 " closed," and repeat the operation as before ; unfcrew 

 the receptacle tor dirty oil O, and fcrew in its place the 

 complete Imall exhaufting iyringe S j work this a few times, 

 and repeat the operation with the barrel and the lever L as 

 before, till the mercury will rife no higher in the gage. 



By the procefs now- defcribed, the cxhauftion has been made 

 fo perfeA, that when an open ciftern barometer, fnfpended m 

 the room, has been on the rife, the mercuiy in the gage G has 

 rifen within -^^ih of an inch as high. 



The double-barrelled air-pump A A being placed on the fame 

 ftand, and having a communication with the pump plate T, as 

 well as the improved pump C, is inteirded for exhaufting large 

 receivers very expeditioufly ; as both pumps maybe worked at 

 the fame time; and moreelpeciallyforpreventingtheimproved 

 pump from being ufed for trifling experiments, or thofe where 

 water is made ule of. In the pump plate T are two holes, 

 fituated near each other, one communicating with the 

 double-barrelled, and the other with the improved pump, 

 and ferving the purpofe of cutting off the communication 

 of either with the receiver at pleafure. Indeed, when the 

 double-barelled pump is only ufed, the hole of the pipe P, 

 leading to the barrel C, ihould always be carefully flopped 

 to prevent moillure of any kind from getting into it. 



Since the time of Mr. Smeaton the air-pump has received 

 very material improvements; for which we are indebted to the 

 Rev. Mr. Prince, of Salem, in North-America; and to Mr. 

 Cuthbertfon, late of Amfterdam, andfince fettled in London. 



Mr. Smeaton's fuccefs in facilitating the opening of the 

 valves, at the bottom of the barrel and in the pifton, led Mr. 

 Prince to conceive, that if thefe valves were entirely re- 

 moved, and the remaining air in the barrel conld be more 

 perfectly expelled, the rarelaclion might be canned ilill far- 

 ther. Upon this plan he conftructed his air-pump. He 

 removed the lower valve, and opened the bottom of the 

 barrel into a ciftern on which it was placed, and which had 

 a free communication with the receiver ; f»rthe valve on the 

 upper plate, at the top of the barrel, conftrufted like Mr. 

 SmeaVon's, made it unneceflary that there fliould be any at 

 the bottom, in order to rarefy the air in the receiver. The 

 ciftern was made deep enough to admit of the pifton's de- 

 fcending into it below the bottom of the barrel. If the 

 piftou be folid, that k, without a valve, when it enters the 

 3 P banel 



